The plural form of abstruseness; multiple instances or types of things that are difficult to understand.
From abstruseness + -es plural suffix. This is simply the regularized plural of the noun abstruseness, following standard English pluralization patterns.
Plural nouns of abstract qualities (like 'abstrusenesses') are rarely used because we usually treat abstruseness as uncountable. When you do see this word, it typically means different kinds or examples of obscurity being discussed separately.
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